Apparently someone did at some point, and it doesn't help. It wouldn't make sense that it would, given that a hard drive is already much faster than the GC/Wii's DVD drive.

OS: Windows 10 64 bit Professional
CPU: Intel i5 4670K @3.4GHz... for now @4.6GHz with a quick and dirty (yet stable) OC. May get faster in a bit before the end of time.
RAM: 16GB (Down from 24 GB after some was given to siblings)
GPU: Radeon Vega 56

The ISO is essentially a disc, and dolphin reads the disc just like the GC or Wii would read a disc drive. Since hard drives are already faster than a disc drive, going to an SSD or a ramdisk wouldn't do much... Especially since dolphin emulates disc drive read speeds now (though that can be disabled for awesome).